terrifying scene in a small town. A train derailment that sent chemicals, a gas called vinyl chloride, spewing into the air. More than 70 people sought medical treatment for burning eyes, labored breathing. And abc's linsey davis is on the scene. Reporter: Thousands of gallons of the chemical vinyl chloride spewed into the air from the ruptured car. Residents were told to stay in their homes. Three schools within a mile ordered to keep students indoors. We are saying to all that are watching this, that live within the burrow of paulsboro, it is a time for caution. Reporter:71 people were admitted to a local opt. Vinyl chloride is a colorless gas. Inhaling it can cause dizziness, headaches and drowsiness. Breathing very high levels can cause loss of consciousness and extremely high levels can even cause death. There have been concerns about this bridge before? I've been told today that the residents most close to that bridge had heard unusual characteristic sounds, clanking sounds. Sounds they don't always hear with that bridge. Reporter: Just three years ago, a coal train derailed on the same bridge. 140,000 miles of straight track across the country, carrying dangerous chemicals near the homes of millimeters of americans. 99.99% of chemical shipments get there safely. But when they don't, the results can be deadly. In south carolina, in 2005, a train carrying chlorine gas exploded. Nine people were killed. Work is expected to continue here, throughout the night. At this moment, the rail cars are being cleaned of the toxin so they can be removed from this area. The ntsb is in the process of documents what happened. They are expected to try to determine the cause of this derailment in the next few days. Diane?

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